This relates generally to imaging devices, and more particularly, to high dynamic range imaging sensor pixels.
Image sensors are commonly used in electronic devices such as cellular telephones, cameras, and computers to capture images. In a typical arrangement, an electronic device is provided with an array of image pixels arranged in pixel rows and pixel columns. Each image pixel in the array includes a photodiode that is coupled to a floating diffusion region via a transfer gate. Column circuitry is coupled to each pixel column for reading out pixel signals from the image pixels. The column circuitry often implements a correlated double sampling (CDS) procedure, which involves obtaining pixel signals by computing the difference between reset signals sampled during reset operations and image signals sampled following charge transfer operations.
An image sensor has an associated dynamic range, which is expressed as a ratio of the largest and smallest possible luminance values for the image sensor. Image sensors are often equipped with high dynamic range (HDR) functionality, in which the image sensors capture images at extended dynamic ranges beyond what would otherwise be possible using image sensors without HDR functionality. One of the most common HDR techniques is multiple exposure imaging. In multiple exposure imaging, multiple images are captured with an image sensor at different exposure times and are later combined into a single high dynamic range image. However, if care is not taken, performing HDR imaging may consume undesirably large amounts of power and may have increased sensor noise levels due to increased dark current from the high power consumption.
It would therefore be desirable to provide improved high dynamic range imaging techniques for image sensors.